﻿    <p>
      An annotation is a graphical representation within the geometric (and spatial) context
      of a project, that adds a note or meaning to the objects which constitutes the project model. Annotations include
      additional points, curves, text, dimensioning, hatching and other forms of graphical notes. It also include symbolic
      representations of additional model components, not representing products or spatial structures, such as survey points,
      contour lines or similar.
    </p>
    <blockquote class="note">
        NOTE&nbsp; Additional presentation information (often 2D) such as tag number or hatching, that is directly
        related to a particular product representation is included within the <em>IfcProductDefinitionShape</em>
        having various <em>IfcShapeRepresentation</em>'s of the <em>IfcElement</em> (and its subtypes). Only those
        presentation information, that cannot be directly related to a single product, have to be wrapped within the
        <em>IfcAnnotation</em>.
    </blockquote>
<p>If available, the annotation should be related to the spatial context of the project, by containing the
      annotation within the appropriate level of the building structure (site, building, storey, or space). This is
      handled by the <em>IfcRelContainedInSpatialStructure</em> relationship.</p>

<p>The <em>IfcAnnotation</em> can provide specific 0D, 1D, and 2D geometric items as representation of the annotation,
offering annotation point, curves, and surfaces. The following values shall be used for the <em>ObjectType</em>.</p>
    <ul>
      <li>
        <b>'Annotation point'</b> is an annotation provided by a point that has additional semantic. The inherited
        attribute <em>ObjectType</em> should be used to capture the type of point annotation, some predefined values are:
        <ul>
          <li>'<b>SurveyPoint</b>: A single survey point represented by a Cartesian point. A property set may add the
          conditions (method, accurracy, etc. to the survey point).
          </li>
          <li>'<b>SurveyArea</b>': A set of survey points represented by Cartesian point. These coordinates are determined 
          relative to the coordinates of a reference point, which acts as the datum for the survey. Properties attached apply
          equally to all points. The difference in elevation of the survey points enables terrain to be determined.<br>
          </li>
        </ul>
      </li>
      <li>
        <b>'Annotation curve'</b> is an annotation provided by a
        curve that has additional semantic. The inherited
        attribute <em>ObjectType</em> should be used to capture the
        type of curve annotation, some predefined values are:
        <ul>
          <li>'<b>ContourLine</b>': A line of constant
          elevation typically used on geographic maps where the
          spacing of lines at constant intervals of elevation may
          be used as an indication of slope.
          </li>
          <li>'<b>IsoBar</b>': A line of constant pressure
          typically used on weather maps or to show pressure
          gradient in spaces, chambers or externally.
          </li>
          <li>'<b>IsoLux</b>': A line of constant illumination
          typically used to show the distribution of illumination
          levels and/or daylighting in a space or externally.
          </li>
          <li>'<b>IsoTherm</b>': A line of constant temperature
          typically used to show the distribution and effect of
          heating or cooling within a space or to show
          temperature distribution on a geographic map.<br>
          </li>
        </ul>
      </li>
      <li>
        <b>'Annotation surface'</b> is an annotation provided by
        a surface that has additional semantic. The inherited
        attribute <em>ObjectType</em> should be used to capture the
        type of surface annotation, some predefined values are:
        <ul>
          <li>'<b>SurveyArea</b>': A surface patch based on survey points.<br>
          </li>
        </ul>
      </li>
    </ul>
<blockquote class="history">HISTORY&nbsp; New entity in IFC2x2.
</blockquote>
